TKOCHOCEEATIDJE. 
25 
surface in the centre of the whorl, but die away partially over the 
front. The whole is so covered with the shell that no septal cha- 
racters are observable, and it is unknown how much belongs to the 
body-chamber. . . . Xo other example of this very distinct form 
has been seen. In shape it is nearest Xautihis qiiadrans^ but its 
ornaments are different.” (Blal-e.) 
Remarhs. This is a well-characterized species, and is now ad- 
mirably represented in the Collection, several specimens having been 
added since the above description was published. Many of these 
show the inner whorls, which are wanting in the type ; there 
are about 2| whorls, with a large central vacuity. Cue of the speci- 
mens has a portion of the shell (about k an inch) projecting in a 
straight direction beyond the coiled ])art, and at its extremity tlie 
rounded margin of the aperture is seen in outline, the shell being- 
half buried in the matrix. The test is marked only with faint 
lines of growth for a distance of about 1 inch before the aperture is 
reached, the annulations becoming a little less prominent just before 
this smooth part begins. 
Horizon. Wenlock Limestone. 
Locality. Dudley, 'VVorcest^^rshire. 
llepresented in the Collection by numerous specimens, including 
the type described and figured by Professor Blake. 
Trochoceras giganteum, J. de C. Sowerby, sp. 
1839. Lituites yiyanteus, J. de C. Sowcrby, in Murchison’s Sil. 8yst. 
pt. ii. G22, pi. xi. f. 4. 
1852. Hortolus yu/anteus, M'Coy, British Pal. Foss, fiisc. ii. p. 324. 
18G5. Trochoceras (jiyanteum, Lyell, Elements of Geology, Gth ed. p. 552. 
1873. Trochoceras (jiyanteum, Salter, Cat. Cambr. aud Sil. Foss, 
pp. IGO, 174. 
1882. Trochoceras yiyanteum, Blake, British Foss. Ceph. pt. i. p. 223, 
pi. xxxi. ff. 1,2. 
Sj>. Char, The shell increases to the extent of about three times 
its own diameter in the last whorl, the latter being out of contact 
with the first whorl for about half its length. “ In several ex- 
amples otherwise agreeing with the type, decided asymmetry is 
observed; in one of the figured specimens (fig. 2) this is associated 
with the peculiar form of aperture to be noticed below. The sub- 
quadrate section is characteristic, though the earlier whorls are 
more rounded. The breadth is always greater than the thickness — 
the proportion increasing with growth. In the other figured 
specimen it reaches a maximum of 22:1 6. The front is usually 
rounded, but tends to become concave. The inside also when out 
of contact retains some concavity. The ribs are rather of irregular 
